Preparation of alkali metal double fluorides of zirconium and hafnium



PREPARATION OF ALKALI META L DOUBLE FLUORIDES OF ZIRCONIUM AND HAFNIUM I Eugene Wainer, Cleveland Heights ,Ohio, assignor, by

mesne assignments, to the United Statesof America as represented by the United States Atomic Energy'Commission l I N Drawing. Application January 31, 1952, Serial No. 269,144 r v 9 Claims. (Cl. 23-'-88) The'double fluorides'of zirconium or hafnium and a base such asammonium, potassium,and sodium, are of importance for commercial applications. These raw materials are used as flux ingredients in non-ferrous and ferrous metallurgy. In view of the wide scale use of these compounds, cost is a major item in determining their ef fectiveness. Known methods of preparing the compounds involve the formation ofa fluorine derivative of zirconium in solution, usually through attack of a raw material with hydrofluoric acid and then precipitating the desired compound through the addition of the proper alkali metal fluoride; All of the reagents used in such a procedure are quite expensive and the end result is that the product iscostly. v

In contrast, the present-inventionis concernedlwith the preparation of alkali metal double fluorides of zirconium or hafnium in a manner avoidiu g high costs, and re- 2 properly"'prepafed, this precipitate is insoluble, *highly crystalline andis readily filtered and may be washed in a slightly acid solution without loss of zirconium value.

' Using such sulfate derivatives of zirconium of the, general nature as described in, the foregoingmy novel method of preparation of the complex fluoride involves the treatment of one or the other of its various sulfates with a fiuorinating agent in the presence of a soluble alkali metal salt which provides the requisite alkali metal. Thus, a

sulfate of zirconium is reacted with material containing fluorine, and an alkaline/earth metal such as calcium, barium or strontium and a base selected from the class consisting of alkali metals and NH4. Of the latter class, potassium and sodium are the metals of practical importance. However, the term alkali metal compound shall be used herein and in the claims as a generic expressulting in products in a range applicable foruses heretofore excluded. The preparation of alkali metal double fluorides of titanium by arelated processjisf de'scribed in my copendingapplicationSerial No..269,143f', filed concurrently herewith. 1

To the accomplishment of'the foregoing and related ends, said invention then 'comprisesthe features hereinafter fully described and particularly pointed out in the claims, the following description setting forth in detail certain illustrative embodimentsof the invention, these being indicative, however, of but a few of vthe various ways in which the principle of the invention may be employed. I

In the usual technology of zirconium, one stage in the sion to include both the alkali metal salts and the ammonium salts. The reactions depend on the insolubilization of the sulfate ion either through the medium of the formation of calcium sulfate or barium sulfate, these being the most available as compared to the strontium compound. For reasons of economy, the calcium derivative is preferred. These reactions may take place under different conditions. Of these, the two most important are '(1) digestion at temperatures in the region of the boiling point of water and (2) a low-temperature heat treatment in the region of 500 to 600 C. followed by leaching" with water. Both procedures are effective and the use of one or the other is determined by the'nat'ure of the endQrequirements. Thus in one series of reactions, at basic zirconium sulfate is dispersed in water and digested with. a mixture of potassium sulfate, sulfuric acid, and fluorspar. The end products of the reaction are'potas- "sium zirconium fluoride and calcium sulfate. In a modi-' fication of this react-ion,- basic zirconium sulfate, sulfuric acid, fluorspar, and potassium sulfate are thoroughly purification, of the element frorn-its' ores usually involves v the preparation of a sulfate derivative which is characterized by its insolubility in water. In any case, the preparation of a basic water insoluble sulfate represents an excellent means for making certain that the compounds in question have been separated from ideleterious impurities such as iron and aluminum.

In the case of zirconium, ,the'formation of basic sul fates of .water insoluble; character is commonly used as a means for purifying a-zireonium raw material. A char acteristic of the basic sulfates of zirconium is the high degree of l-insolubility in water or inacid media. The basic sulfates may be transformed. to the normal sulfate through the addition of the requisite amount of sulfuric acidorto an alkali metal double sulfate by the addition of a mixture of sulfuric acid and alkali metal sulfate. In any case, these represent logical starting agents for the preparation-of other compounds. v

p The normal sulfate of zirconium contains two moles of sulfuric acid to one mole of zirconia, this being the requirement for complete water solubility. Generally any ratio less than this amount leads to water insolubility. The compoundnormally obtained by the usual methods of hydrolytic separation of zirconium is the one in which theratio of the zirconia to sulfate ion is of the value varying between 3 to 2 and 5 to 2 and the average ratio most commonly encountered is the ratio 5 to '3. When mixed in paste form, the paste dried, and then the mixture is calcined at a temperature between 500 and .600" C. for about an hour; and in still a further modification of this reaction, the materials are thoroughly mixed in dry form and then calcined at temperatures of 500 to 600 C.

Other fiuorinating agents may 'be used in place of the fluorspar and of these, the most important are the fluosilicates of sodium, potassium or ammonium, and again in this case, the reaction may be carried to completion by digestion at temperatures close to 100 C. or through reaction at elevated temperatures in the region of 500 to 600 C. When the fiuosilicates are used as fiuo'rinating agents, a specific series of steps are required to obtain the desired results involving chiefly a contact between the fluorinating agent and the zirconium sulfate first, followed by treatment with a sulfate insolubilizing agent such as alkaline earth compounds, e. g. calcium, barium, or strontium compounds in order to obtain the desired results. If desired, combinations of fluosilicates and fluorides may be used for the purpose.

I From a material standpoint, suitable sulfates of zirconium for the purposes of these reactions are the basic sulfate, the normal sulfate, and an alkali metal double sulfate of sodium or potassium. The major differences imposed by virtue of the differences in the nature of the starting agents is the replenishment of the alkali or sulfate ion which might be required in order to provide sufficient material for completionof the reactions to be given hereinafter.

With respect to the alkali metal, this may be supplied as-water soluble salts of ammonium, sodium, or potassium depending on which complex fluoride is desired. If the ammonium salt is used, only those reactions which take place through the medium of digestion below C. are effective since calcination decomposes the ammonium usually moreeifective to use the basic sulfate derivatives of the zirconium since these may be more readily dried than the normal sulfates. Under these conditions, a complete mixture is possible without too much difliculty. On calcination, a sinter is obtained in the region of 600 to 700' C. After leaching, the complex zirconiumfluoride is obtained in the filtrate, and the silica'and calcium sulfate are separated out as. precipitates. Again as before, a slight excess of fluoride ion is provided in the reactants to make certain that ahydrated compound of zirconium will not be prepared. In the case of the reactions involving the complex fluosilicates'as fluorinatingagents, the calcination reaction is the preferred one since when the reaction is completed through normal digestionzitechniques, the gelatinous silica formed makes it somewhat difiicult to separate the precipitate from the desired reagents with the requisite ease.

In carrying out these various reactions, it. is always a requirement that the reaction remain slightly on the acid side, and in the presence of a slight excess of'fluoride ion. In this way, the formation of basic fluorides or of hydrates of zirconium is prevented.

I 'If carried out in accordance with this system, the yields 7 are normally in excess of 90%. This yield is best determinedyby evaporating the solution containing the salts completely to dryness since the major portion of the loss in yield is developed through the recrystallization requirement.

The reactions involved here, and the same procedures arelikewise applicable to hafnium, accordingly, the features as herein described are also to be considered as concerning hafnium.

- Having described my invention in general, terms, the following examples are illustrative of recommended practice:. Example ].-'-132 grams of basic zirconium sulfate, equivalentto 62 grams of zirconium dioxide 'are dispersed in 200 cc. of water and stirred. 90% sulfuric acid is then added todigest the zirconium sulfate an'd stirring continued. In a separate container, 54 grams of potassium sulfate, and 2 grams of KFlare dissolved in400zcc. of hotwater and this solution is then added slowly with stirring to the acid zirconium sulfate solution 62 grams of 325 mesh fluorspar is then slurried in 100 cc. of water and this slurry added to'the potassium zirconium acid sulfate solution. The stirring iscontinued for about 15 minutes and the solution is then heated until a temperature of approximately 90 C. is obtained. With occasional stirring, the heating is'continued for 2 hours, after which the level of the solution is diluted to an approximate volume of 2 liters, and thedigestion is continued for several minutes more. A coarse precipitate is formed in the solution and while still maintained in the hot condition, the liquid is allowed to settle quietly without stirring until the supernatant liquid is clear. The clear liquid is I T 6 I amount of product. 'Ingeneral for potassium zirconium fluoride,--the solutions may 'be evaporated to about 200 cc. before cooling is commenced. If the drying is carriedv out above 100 C., the potassium zirconium fluoride will lose a molecule of water, in which case the weight yields will be approximately 7% less, due to this water loss. V.

Example 2.-.-36 grams of normal zirconium sulfate of tinned for a few minutes more, after which 1 liter of hot water is added and the temperature of the liquid is then increased to about 90 C. The digestion is continued for about 2 hours, at which point the solution is diluted to -l500'cc. while still maintaining the/temperature at 90 to 95 C. The stirring is stopped and the solution is allowed to clarify by settling and decantation. The precipitated calcium sulfate is removed, and approximately grams of product is obtained from the first batch of 1 crystals on drying at .85 C. Evaporation of the first '1, wash water from the crystals yields another few grams.

enough to be stirred, and, on grinding together in an intensive mixer the mix stiffens to ahard cementitious type mass. This mass is broken out-of thefmixerand thrown into a furnace heated to about 600 C. The material iscalcined at this temperature for about an hour and a*half, and the hard sinteris then discharged. The sinter is ground to a powder and dispersed in. 4. liters of hot water and then digestion in hot water is continued for about an hour. potassium zirconium fluoride in, solution and calcium sulfate as'a precipitate, and these are separated in the manner of Example 1. ;The yield of potasium zirconium settling and decantation, the clear liquid is added to the original filtrate. The crystals are then thrown on an'acid proof filter and dewatered as completely as possible, afterwhich the crystals are washed once with 100 cc. of hot water of composition similar to the first wash water. All of the filtrates are combined and evaporated to a volume such that evident crystallization is taking place. This usually is observed at a volume of less than 500 cc. The solution is then cooled to about 10 C., during which 'a crop of White coarse crystals develops. These crystals are dewatered in a centrifuge and then dried. The liquor from the first centrifuging is retained to be used as the mother liquor in a subsequent crystallization. If the drying is accomplished at a temperatureless than 80 C., about 80 grams of crystallized product of the formula K2ZrFe is the yield. Evaporation of the liquid recovered from the centrifuge to dryness will provide a further fl lO ide is about 270 grams. Example 4.355 grams of normal zirconium sulfatev 225 grams ofpotasis dissolved in a liter. of hot water. sium fluosilicate and 10 grams of potassium fluoride in finelypowdered form are added to the water solution and the whole is digested at about C. for about 1 hour. A slurry is prepared in a separate container of 200 grams of precipitated calcium carbonate in 500cc. of water and this slurry is slowly added to the stirred orig inal solution of the fluosilicate and fluoride and zirconium sulfate. C. for another hour to an hour and a half, and is then diluted with hot water to a total volume of about 10 liters. After digesting in this diluted condition for 30 to 50 minutes, the stirring is stopped and while maintaining the solution hot the precipitate is allowed to settle. I

The liquid containing the precipitate is freed of precipitate by settling, decantation, filtration, and washing. Concentration of the clarified wash liquors is accomplished by evaporation toa volume of approximately 1 liter and the relatively thick liquid is then allowed to cool to room temperature. A well crystallized crop of crystals in yield of about 275 grams is obtained after centrifuging The end" products of thereaction are The solution is then digested at 90 to 7 Other modes of applying the principle of the invention maybe eniployed-, change being made as regards the de tails described, provided the features stated in any of the following claims or the equivalent of such be employed. I therefore particularly point out and distinctly claim asmy invention:

1-. The method of producing a double fluoride of an alkali metal and a metal of the group consisting of z irconium and hafnium from an iron-free sulfate of said metal which comprises directly and concurrently reacting said sulfatewith a source of combined alkali metal and combined alkaline earth metal and combined fluorine provided by at least one alkaline earth compound other than the fluozirconates and fluohafnates and atleast one alkli metal compound other than the fluoz irconates and fluohafnates separating the resulting alkaline earth sulfate; and recovering the resulting double fluoride ofsaid metal and said alkali metal. i 2. 'I he methodof claim 1 in which one of the reactants is an alkaline earth fluoride.

3. The method of claim 1 in which one ofthe reactants is an alkali metal fluosilicate.

4; The method of producing a double fluoride of an alkali metal and a metal of the group consisting of zirconium and hafnium from an iron-free sulfate of said metal which comprises: digesting said sulfate in an aqueous medium at about the boiling point with a source ofcombined alkali metal and combined alkaline earth metal and combined fluorine provided by at least one alkaline earth metal compound other than the fluozirconates and fluohafnates andat least one water soluble alkali metal compound other than the fiuozirconates and fluohafnates; separating the resulting aqueous medium from the insolubles; and recovering the-dissolved double fluoride-ofsa-id metal and saidalkali metal from the separated aqueous medium.

5. The method of producing a double fluoride of an alkali metal and a metal of the group consisting of zir-' conium and hafnium from an iron free sulfate of said metal which comprises: digesting said sulfate in an aqueous medium at about the boiling point with at least one alkaline earth metal fluoride and at least one water soluble alkali metal compound otherthan the fluozirconates and fluohafnates, separating the resulting aqueous medium from the insolubles; and recovering the dissolved double fluoride of said metal and said alkali metal from the separated aqueous medium.

6. The method of producing a double fluoride of an alkali metal and a metal of the group consisting of zirconium and hafnium from an iron-free sulfate of said metal which comprises: digesting said sulfate in an aqueous medium at about the boiling point with at leastone alkali metal fluosilicate and at least one alkaline earth compound other than the fluozirconates and fluohafnates, separating the resulting aqueous medium from the insolubles; and recovering the dissolved double fluoride of said metal and said alkali metal from the separated aqueous medium.

7. Te method of producing a double 'fluoride of an alkali metal and a metal of the group consisting of zirconium and hafnium from an iron-free sulfate of said metal which comprises: calcining said sulfate at a temperatu-re of about 600 C; with a source of combined alkali metal and combined alkaline earth metal and combined fluorine provided by at least one alkaline earth compound other-than the fluozirconates and fluohafnates and at least one alkali metal compound other than the fluozirconates and fluohafnates and which is' not appreciably volatile at about-600 C.; leaching the calcined mass with'an aqueous medium; separating the resulting leach liquor from the insolubles; and recovering said double fluoride of said metaland said alkali metal from the separated leach liquor.

8. Thev method of producing a double fluoride of an alkali metal and a metal of the group consisting of zirconium and hafnium from an iron-free sulfate of said metal which comprises: calcining said sulfate at a temperature of about 600 C. with at least one alkaline earth fluoride and at least one alkali metal compound other than the. fluozir-conates and fluohafnates and which is not appreciably volatile at about 600 C.; leaching the calcined mass with an aqueous medium; separating the resulting leach liquor from the insolubles; and recovering said 5 doublefluoride of said metal and said alkali metal from the separated leach liquor.

9. The method of producing a double fluoride of an alkali metal and a metal of the group consisting of zirconium andahafnium from an iron-free sulfate of said metal which comprises: calcining said sulfate at a temperature of about 6009 C. with at least one alkaline earth compound other than the fluozirconates and fluohafnates and at least one alkali metal fluosilicate which is notappreciably. volatile. at about 600 C.; leaching the calcined mass .with an aqueous medium; separating the resulting leach liquor from the insolubles; and recovering said double. fluoride .of said metal and said alkali metal from the separated leach liquor.

References Cited in the file of this patent UNITED STATES PATENTS 

1. THE METHOD OF PRODUCING A DOUBLE FLUORIDE OF AN AKALI METAL AND A METAL OF THE GROUP CONSISTING OF ZIRCONIUM AND HAFNIUM FROM AN IRON-FREE SULFATE OF SAID METAL WHICH COMPRISES DIRECTLY AND CONCURRENTLY REACTING SAID SULFATE WITH A SOURCE OF COMBINED ALKALI METAL AND COMBINED ALKALINE EARTH METAL AND COMBINED FLUORINE PROVIDED BY AT LEAST ONE ALKALINE EARTH COMPOUND OTHER THAN THE FLUOZIRCONATES AND FLUOHAFNATES AND AT LEAST ONE ALKLI METAL COMPOUND OTHER THAN THE FLUOZIRCONATES AND FLUOHAFNATES SEPARATING THE RESULTING ALKALINE EARTH SULFATE; AND RECOVERING THE RESULTING DOUBLE FLUORIDE OF SAID METAL AND SAID ALKALI METAL. 